1. Field of the Invention
The present invention relates to a blood flowmeter. More particularly, it relates to the blood flowmeter utilizing an ultrasonic continuous wave and having a Doppler effect.
2. Description of the Related Art
Blood flowmeters are widely used in the diagnosis of a living body, in the field of medical instruments, and are able to measure blood stream volume and distribution flowing in a blood vessel without exposure or cutting of the blood vessel.
Two known types of blood flowmeters utilize an electromagnetic effect and an ultrasonic wave, and these types of blood flowmeters basically have the same structure as that of a flowmeter used as industrial equipment. In a blood flowmeter using an ultrasonic wave, a Doppler effect is generally utilized for measuring blood stream volume. That is, the blood stream volume can be obtained by irradiating the ultrasonic wave and measuring the frequency shift quantity between a reflected wave and a transmitted wave.
There are two types of ultrasonic waves used in this field, a pulse wave and a continuous wave (CW). The present invention refers to the CW type ultrasonic wave device.